1. Field of the Invention
The present invention relates to a discharge cell used for a plate-type ozonizer and its manufacturing method.
2. Discussion of the Background
FIG. 8 shows a conventional discharge cell used for a plate-type ozonizer. The discharge cell includes a planar high-voltage electrode 1 and a planar ground electrode 2 arranged so as to face each other at a predetermined interval. Dielectrics 3 and 3' are formed on the facing surfaces of the high-voltage electrode 1 and ground electrode 2 by means of coating. Moreover, a spacer 5 is set between the dielectrics 3 and 3' to form a discharge space 4 having a predetermined gap.
In addition, heat sinks 6 and 7 are included in close contact on the outside of the high-voltage electrode 1 and ground electrode 2. The heat sink 6 at the high-voltage electrode 1 is connected with a high-voltage terminal of a high-voltage power supply 8 and the heat sink 7 at the ground electrode 2 is ground together with a ground terminal of the high-voltage power supply 8.
To produce ozone, a high voltage is applied between the high-voltage electrode 1 and the ground electrode 2 by the high-voltage power supply 8 connected to the beat sinks 6 and 7. Thus, a silent discharge is generated in the discharge space 4 between the dielectrics 3 and 3'. By circulating a material gas, such as an oxygen gas or air through the discharge space 4 under the above state, some of the material gas is exposed to the silent discharge and ozonized.
A plate-type ozonizer frequently uses a plurality of the above-mentioned discharge cells by using each discharge cell as one module and superimposing the discharge cells in a thickness direction.
However, the above conventional ozonizer discharge cell has the following problems.
To form the discharge space 4 having the predetermined gap between the dielectrics 3 and 3', the spacer 5 is set between the dielectrics 3 and 3'. The spacer 5 includes an elastic silicon sheet to protect the dielectrics 3 and 3' from a tightening force when superimposing a plurality of discharge cells. This is because, if the spacer 5 is hard, the dielectrics 3 and 3' may be broken due to the force produced when a plurality of discharge cells are superimposed and tightened.
In addition, ozone has an oxidation capacity similar to that of fluorine among natural oxidizing agents. Therefore, even though a silicon sheet is superior in oxidation resistance, the silicon sheet is unavoidably changed in properties or deteriorated in quality due to the oxidation capacity after exposure to ozone for a long time. Thus, a conventional discharge cell has a durability problem.
In addition, the spacer 5 is bonded to the dielectrics 3 and 3' by an adhesive to secure an airtightness of the discharge space 4. However, because the bonding force is not large, a pressure of a material gas circulating through the discharge space 4 is limited.
Further, the high-voltage electrode 1 and ground electrode 2 produce heat from the discharge energy of the generated silent discharge. This heat causes a lower ozone producing efficiency because the heat accelerates a dissolution of produced ozone. To improve the above problem, the heat sinks 6 and 7 are placed directly on the high-voltage electrode 1 and ground electrode 2 or are placed on the electrodes 1 and 2 through a sheet, such as an aluminum foil which is superior in heat conductivity.
In this case, the heat sink 7 at the ground electrode 2 is a water-cooled type having a high cooling efficiency. In addition, the heat sink 6 at the high-voltage electrode 1 is an air-cooled type to prevent a short circuit due to cooling water having a low insulation resistivity. However, the air-cooled type heat sink is inferior to the water-cooled type in cooling efficiency. Therefore, in the case of a conventional discharge cell, the ozone producing efficiency is unavoidably lowered.
Moreover, the heat sinks 6 and 7 are large compared to other component members and the air-cooled-type heat sink 6 is particularly large. Therefore, it is difficult to reduce a size of a discharge cell.